Ultrasonic probe, and photoacoustic-ultrasonic system and inspection object imaging apparatus including the ultrasonic probe

ABSTRACT

Provided are an ultrasonic probe capable of forming an image without degradation even when the frequency band of a photoacoustic wave and the frequency band of an ultrasonic wave used in ultrasonography are separated from each other, and an inspection object imaging apparatus including the ultrasonic probe. The ultrasonic probe includes a first array device capable of transmitting and receiving an ultrasonic wave; and a second array device capable of receiving a photoacoustic wave. The first array device includes plural electromechanical transducers arranged in a direction perpendicular to a scanning direction, the second array device includes plural electromechanical transducers arranged in a two-dimensional manner, and the first array device and the second array device are provided on the same plane and in the scanning direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 12/999,303, filed Dec. 15, 2010, which is a U.S. national stageapplication of International Patent Application No. PCT/JP2009/061434,filed Jun. 17, 2009, which claims the priority benefit of JapanesePatent Applications No. 2008-159314, filed Jun. 18, 2008, and No.2009-136365, filed Jun. 5, 2009, all of which are hereby incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to an ultrasonic probe for transmittingand receiving an ultrasonic wave and for receiving a photoacoustic wave,and to a photoacoustic-ultrasonic system and an inspection objectimaging apparatus including the ultrasonic probe.

BACKGROUND ART

A conventional tomographic imaging apparatus which obtains a tomographicimage using an ultrasonic wave includes: a probe for transmitting anultrasonic wave to a sample and receiving the reflected ultrasonic wave;a transmitting portion for supplying an ultrasonic signal to the probe;a receiving portion for receiving the reflected wave; and a unit forconverting the received reflected wave signal into a luminance signalfor visualization. When a time-series tomographic image acquired by theapparatus is used, it is possible to observe an inside of a sample. Inthe apparatus according to one mode, a unit for performing scanning of aprobe two-dimensionally scans a sample with an ultrasonic wave to obtaina three-dimensional image.

Meanwhile, in examining an inspection object, apparatuses which displaynot only a morphologic image but also a functional image haveprogressively been developed in recent years. As one of such apparatusesas described above, there is an apparatus which utilizes a photoacousticspectroscopy. In the photoacoustic spectroscopy, visible light,near-infrared light, or mid-infrared light each having a predeterminedwavelength is applied to the inspection object. Then, a specificsubstance inside the inspection object absorbs energy of the appliedlight, and as a result of the absorption, an elastic wave (photoacousticwave) is generated and detected. In this manner, concentration of thespecific substance is quantitatively measured. The specific substanceinside the inspection object is, for example, glucose or hemoglobincontained in blood. A technology of acquiring a photoacoustic imagethrough the photoacoustic spectroscopy is disclosed in, for example,Japanese Patent Application Laid-Open No. 2001-507952. The technology isreferred to as a photoacoustic tomography (PAT).

In addition, Japanese Patent Application Laid-Open No. 2005-021380discloses a method of reconstructing both a photoacoustic image and anormal ultrasonic echo image using a one-dimensionally-arrangedelectromechanical transducer which is common to the both images; and astructure in which a lighting system using a glass fiber is providedbetween one-dimensionally-arranged electromechanical transducers.According to Japanese Patent Application Laid-Open No. 2005-021380, theultrasonic echo image and the photoacoustic image are simultaneouslyacquired, thereby displaying a morphologic image and a functional image.In this case, a common probe is used to transmit and receive anultrasonic wave for forming the ultrasonic echo image and to receive aphotoacoustic wave for forming the photoacoustic image.

It should be noted herein that an elastic wave generated by thephotoacoustic spectroscopy (photoacoustic imaging method) is referred toas a photoacoustic wave, and a sonic wave which is transmitted andreceived in a normal pulse echo method is referred to as an ultrasonicwave.

The frequency band of a photoacoustic wave used in the photoacousticspectroscopy is generally lower than the frequency band of an ultrasonicwave used in ultrasonography. For example, the frequency band of thephotoacoustic wave is distributed within a range of 200 KHz to 2 MHzwith 1 MHz being a center frequency. The distribution of the frequencyband of the photoacoustic wave is lower than a center frequency of 3.5MHz of the ultrasonic wave used in ultrasonography. According toJapanese Patent Application Laid-Open No. 2005-021380, the common probeis used to receive the photoacoustic wave and the ultrasonic wave usedin ultrasonography.

However, as described in Japanese Patent Application Laid-Open No.2005-021380, when the common probe is used to receive the photoacousticwave and the ultrasonic wave which have frequency bands different fromeach other, there arises a problem that spatial resolution isdeteriorated in the ultrasonic image. In order to solve theabove-mentioned problem, a harmonic imaging method is used in JapanesePatent Application Laid-Open No. 2005-021380. However, a signalcontained in a harmonic component is attenuated more than a signalcontained in a fundamental component, and hence there is a fear thatsensitivity may be decreased.

In a case where the frequency band of the photoacoustic wave and thefrequency band of the ultrasonic wave are remarkably separated from eachother (for example, the center frequency band of the photoacoustic waveis approximately 1 MHz and the center frequency band of the ultrasonicwave is approximately 10 MHz), the above-mentioned problem becomes moreremarkable when the common probe is used to receive the waves asdescribed in Japanese Patent Application Laid-Open No. 2005-021380.

Moreover, with regard to a photoacoustic-ultrasonic system including anultrasonic probe and an optical system, the following problem arises.Specifically, according to Japanese Patent Application Laid-Open No.2005-021380, for generation of a photoacoustic wave, a laser light isintroduced using an optical fiber. However, in order to generate thephotoacoustic wave, an extremely strong laser light is required, whichmay adversely affect the fiber. Particularly, when a sample is thick sothat light is attenuated to a large degree, the above-mentioned problembecomes more serious.

According to an experiment conducted by the inventors of the presentinvention using a dummy inspection object, it was found that, in orderto generate a photoacoustic wave strong enough to detect a sample havinga thickness exceeding the order of “cm”, the intensity of the laserlight introduced into the optical fiber exceeds several tens kJ/cm²,which increases a burden on the optical fiber. Therefore, the opticalfiber may not be selected as the optical system for detecting a samplehaving a certain volume.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an ultrasonic probecapable of forming an image without degradation even when a frequencyband of a photoacoustic wave and a frequency band of an ultrasonic waveused in ultrasonography are separated from each other, and an inspectionobject imaging apparatus including the ultrasonic probe.

Another object of the present invention is to provide aphotoacoustic-ultrasonic system including the ultrasonic probe and anoptical system, which is capable of applying pulse light having a stronglight intensity for detecting a sufficient photoacoustic wave.

In view of the above-mentioned objects, the present invention providesan ultrasonic probe, comprising: a first array device capable oftransmitting and receiving an ultrasonic wave; and a second array devicecapable of receiving a photoacoustic wave, wherein the first arraydevice includes plural electromechanical transducers arranged in a firstdirection; the second array device includes plural electromechanicaltransducers arranged two-dimensionally; and the first array device andthe second array device are provided on the same plane and in a seconddirection perpendicular to the first direction.

The present invention also provides a photoacoustic-ultrasonic system,comprising: an optical system for introducing light emitted from a lightsource into an inspection object; and the ultrasonic probe, wherein theoptical system is provided in an interspace between the first arraydevice and the second array device.

The present invention also provides an inspection object imagingapparatus, comprising: a light source for generating pulse light; theultrasonic probe; and a system control unit for controlling the lightsource and the ultrasonic probe to form an image. The system controlunit forms an image based on morphologic information inside aninspection object by using the first array device and forms an imagebased on functional information inside the inspection object by usingthe light source and the second array device.

According to the present invention, there can be provided an ultrasonicprobe capable of forming an image without degradation even when thefrequency band of the photoacoustic wave and the frequency band of theultrasonic wave used in ultrasonography are separated from each other,and an inspection object imaging apparatus including the ultrasonicprobe.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view illustrating an ultrasonic probe according to anembodiment of the present invention;

FIG. 1B is a view illustrating an arrangement of an ultrasonictransducer and a photoacoustic transducer which form a transducer usedin the ultrasonic probe according to the embodiment of the presentinvention;

FIG. 2 is a diagram illustrating a configuration of an inspection objectimaging apparatus including the ultrasonic probe according to theembodiment of the present invention;

FIG. 3 is a diagram for describing a signal collection method using theultrasonic probe according to the embodiment of the present invention;

FIG. 4 is a diagram illustrating a beam shape of the ultrasonictransducer according to the present invention;

FIG. 5 is a diagram illustrating a beam shape of the ultrasonictransducer in a height direction thereof according to the presentinvention;

FIG. 6 is a graph illustrating a relation between the ultrasonic probeand a beam thickness of the ultrasonic transducer in the heightdirection according to the present invention;

FIG. 7A is a perspective view illustrating a photoacoustic-ultrasonicsystem including an ultrasonic probe and an optical system according toanother embodiment of the present invention; and

FIG. 7B is a cross-sectional view of the photoacoustic-ultrasonicsystem, which illustrates incidence of light.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention are now described indetail in accordance with the accompanying drawings.

Hereinafter, the present invention is described in more detail withreference to the accompanying drawings. It should be noted that the samecomponents are denoted by the same reference symbol in general, anddescription thereof is omitted.

First Embodiment Ultrasonic Probe and Inspection Object ImagingApparatus

An ultrasonic probe according to this embodiment includes a first arraydevice capable of transmitting and receiving an ultrasonic wave; and asecond array device capable of receiving a photoacoustic wave. The firstarray device includes plural electromechanical transducers arranged in afirst direction. The second array device includes pluralelectromechanical transducers arranged two-dimensionally. The firstarray device and the second array device are provided on the same planeand in a second direction. In the present invention, the “same plane” isnot necessarily required to be strictly the same plane as long as theplane can be regarded as substantially the same plane. In the definitionof “substantially the same plane”, it is acceptable that the plane onwhich the array devices are provided includes irregularities within arange of processing accuracy and includes inclination or leveldifference as long as the contact condition between an inspection objectand the array device is not adversely affected. Even when irregularitiesor the like are intentionally provided on a surface of the plane inorder to reduce contact resistance with the inspection object, similarlyto the above-mentioned case, the irregularities or the like areacceptable as long as the contact condition between the inspectionobject and the array device is not adversely affected.

In the ultrasonic probe and an inspection object imaging apparatusincluding the ultrasonic probe according to this embodiment, the seconddirection is typically a scanning direction and the first direction istypically a direction perpendicular to the scanning direction.

The ultrasonic probe and the inspection object imaging apparatusincluding the ultrasonic probe according to this embodiment may acquirean image of the inspection object even in a rest state without scanningthe first array device and the second array device.

Hereinafter, description is specifically made with reference to theaccompanying drawings. FIGS. 1A and 1B are structural views of theultrasonic probe according to the present invention. FIG. 1A is aschematic view and FIG. 1B is an enlarged view illustrating a transducerportion. The ultrasonic probe includes a probe case 30, a cable 31, anda transducer 4. The transducer 4 is comprised of an ultrasonictransducer 4 a which is the first array device capable of transmittingand receiving an ultrasonic wave; and a photoacoustic transducer 4 bwhich is the second array device capable of receiving a photoacousticwave. A one-dimensional (linear) array is employed for the ultrasonictransducer 4 a while a two-dimensional array is employed for thephotoacoustic transducer 4 b.

The ultrasonic transducer 4 a is used for revealing morphologicinformation of the inside of the inspection object, and therefore is atransducer capable of transmitting and receiving an ultrasonic wavehigher in frequency than a photoacoustic wave received by thephotoacoustic transducer 4 b which acquires functional information.Here, the frequency band of the ultrasonic transducer 4 a is 7 to 12 MHzas a typical value. The “morphologic information” is information whichis based on a morphology of the inside of the inspection object andobtained by a normal pulse echo method.

On the other hand, the photoacoustic transducer 4 b is used forrevealing functional information of the inside of the inspection object,and therefore is a transducer capable of receiving an ultrasonic wave(photoacoustic wave) lower in frequency than an ultrasonic wavetransmitted and received by the ultrasonic transducer 4 a which acquiresmorphologic information. Here, the frequency band of the photoacoustictransducer 4 b is 1 to 4 MHz as a typical value. The “functionalinformation” is information which is obtained by a photoacousticspectroscopy (photoacoustic imaging method) and relates to concentrationof a specific substance inside the inspection object, such as glucose orhemoglobin contained in blood.

The reason why the one-dimensional array is employed for the ultrasonictransducer 4 a is as follows. The ultrasonic transducer 4 a transmitsand receives an ultrasonic wave having a relatively high frequency, andhence the device density thereof needs to be made high. For example, thenumber of transducer arrays is as large as 128 to 256 even in theone-dimensional array. Therefore, when the two-dimensional array isemployed for the ultrasonic transducer 4 a, it is not appropriate interms of costs.

The main reason why the two-dimensional array is employed for thephotoacoustic transducer 4 b is that light utilization efficiency isregarded as important. Specifically, when photoacoustic waves generatedby one irradiation with laser light are received bytwo-dimensionally-arranged devices, larger number of photoacoustic wavescan be received compared with a case where the devices areone-dimensionally arranged. The photoacoustic wave is generally lower infrequency than an ultrasonic echo, and hence the device density can besuppressed to be small. Accordingly, the two-dimensional array has asmall influence on costs. The number of transducer arrays in one line isapproximately 10 to 50.

The ultrasonic transducer 4 a includes the plural electromechanicaltransducers. The electromechanical transducer is a device which conductsmutual conversion between an electrical signal and a mechanicalvibration (ultrasonic wave), and, for example, a piezoelectric device isused therefor. The plural electromechanical transducers are arranged ina direction (first direction) perpendicular to the scanning direction.

The photoacoustic transducer 4 b is a device in which theelectromechanical transducers are two-dimensionally arranged. Examplesof the electromechanical transducer include a transducer using apiezoelectric phenomenon, a transducer using optical resonance, and atransducer using a change in capacity. Any detector may be employed asthe electromechanical transducer as long as the detector can detect anacoustic wave. In a case where sizes of detection targets vary widely,bands of generated photoacoustic waves are also widened, and hence arequired transducer favorably has a wide detection band. Inconsideration of the above-mentioned aspect, an electrostatic capacitytype ultrasonic transducer, which has actively been studied in recentyears, is one of most suitable transducers for the object of the presentinvention. Alternatively, when a device in which plural transducershaving different detection bands are combined is employed, the sameeffect can be expected.

The ultrasonic probe according to this embodiment is manufactured in thefollowing manner. First, the ultrasonic transducer 4 a (one-dimensionalarray transducer) and the photoacoustic transducer 4 b (two-dimensionalarray transducer) are manufactured by a method similar to theconventional method. The method includes cutting out a piezoelectrictransducer; fixing the transducer to a backing material; dicing thetransducer; bonding an acoustic matching layer; and leading out a wiringportion. In addition, an acoustic lens is attached to the ultrasonictransducer.

The ultrasonic transducer and the photoacoustic transducer are arrangedwith a space therebetween, and then fixed by molding. After that, theultrasonic transducer and the photoacoustic transducer are fit into ahousing, whereby the ultrasonic probe is completed.

The acoustic matching layer, the backing, and the wiring are provided onan upper surface and a lower surface of each of the transducers, and theacoustic lens is provided on the upper surface of the ultrasonictransducer. Those components are omitted in FIGS. 1A and 1B.

The ultrasonic transducer 4 a and the photoacoustic transducer 4 b havea positional relation in which the ultrasonic transducer 4 a is providedin parallel to any one of four sides of the photoacoustic transducer 4 bwhich is two-dimensionally arrayed. In this embodiment, the two arraydevices are housed in one probe case 30. Alternatively, a probe casethat houses the ultrasonic transducer 4 a and a probe case that housesthe photoacoustic transducer 4 b may be provided to form one probe as awhole. In this case, the two array devices are only required to be onthe same plane and may be located with a certain space therebetween.

FIG. 2 is a block diagram illustrating an inspection object imagingapparatus using the ultrasonic probe according to this embodiment. Inorder to transmit an ultrasonic wave from the ultrasonic transducer 4 a,an ultrasonic signal is generated through a system control unit 1, atransmission beam former 2, and a transmission amplifier 3, and then avoltage is applied to the ultrasonic transducer 4 a. The transmittedultrasonic wave is reflected on an inspection object 14 and received bythe ultrasonic transducer 4 a. The received ultrasonic signal, each ofthe signals of the respective devices in the ultrasonic probe, issubjected to phasing addition through a reception amplifier 5 and areception beam former 6. The reception beam former 6 performsanalog-digital conversion, delay, and weighting control. Then, theultrasonic signal is detected and converted into a luminance signal byan ultrasonic signal processing unit 10, and is accumulated in an imagememory within an image processing unit 11.

On the other hand, a photoacoustic wave is detected in the followingmanner. A light source 13 irradiates the inspection object 14 with pulselaser light. The pulse laser light is emitted by transmitting a drivesignal from the system control unit 1 to the light source 13. When theinspection object 14 is irradiated with the pulse laser light, adetection target inside the inspection object 14, such as hemoglobin,absorbs energy of the laser light. The temperature of the detectiontarget rises in accordance with the amount of the absorbed energy. As aresult of the temperature rise, the detection target momentarily expandsto generate an elastic wave (photoacoustic wave). The generatedphotoacoustic wave is received by the photoacoustic transducer 4 b,passes through a reception amplifier 7 and an analog-digital converter8, and then is subjected to an image reconstruction processing by aphotoacoustic signal processing unit 9. The reconstructed photoacousticsignal is accumulated as a luminance signal in the image memory withinthe image processing unit 11.

Then, the image processing unit 11 superimposes the accumulatedultrasonic signals on the accumulated photoacoustic signals followed byimage display by an image display unit 12.

Next, a method of acquiring three-dimensional signals of an ultrasonicsignal and a photoacoustic signal with the use of the ultrasonic probeaccording to this embodiment is described. As described above, theone-dimensional array is employed for the ultrasonic transducer and thetwo-dimensional array is employed for the photoacoustic transducer, andhence, in order to acquire volume data with the use of the ultrasonicprobe according to this embodiment, scanning is performed with theultrasonic probe.

FIG. 3 is a conceptual diagram of scanning performed with the ultrasonicprobe according to this embodiment, and illustrates scanning areas 20 a,20 b, and 20 c. In the scanning, the ultrasonic probe is moved in thesecond direction (X direction of FIG. 3) in which the ultrasonictransducer 4 a and the photoacoustic transducer 4 b are arranged. Whenthe scanning of the scanning area 20 a is finished, the ultrasonic probeis moved in a longitudinal direction (Y direction of FIG. 3) by a stripewidth of the scanning area and then is moved over the scanning area 20 bin the opposite direction. The above-mentioned scanning is repeatedlyperformed, whereby signals of an entire inspection area are acquired.

The following three patterns of methods are conceivable for thescanning: (a) a method in which a photoacoustic signal is acquiredduring a stage suspension period and an ultrasonic signal is acquiredduring a stage moving period; (b) a method in which a photoacousticsignal and an ultrasonic signal are both acquired during the stagesuspension period; and (c) a method in which a photoacoustic signal andan ultrasonic signal are both acquired during the stage moving period.The same signals can be acquired by any one of the above-mentionedmethods.

First, in the method (a) in which the photoacoustic signal is acquiredduring the stage suspension period and the ultrasonic signal is acquiredduring the stage moving period, the pulse laser is irradiated during thestage suspension period to acquire the photoacoustic signal. After that,the ultrasonic signals are continuously transmitted and received duringthe stage moving period, and a process of acquiring a slice image ateach position is repeated. In this case, for example, the length of thephotoacoustic transducer 4 b in the scanning direction (X direction) istaken as one step width, and one set of pulse laser irradiation,photoacoustic signal detection and moving by one-step width is repeated.When the transducer 4 is moved by the one-step width, the ultrasonicwave is acquired using the ultrasonic transducer 4 a. The step width ofthe transducer 4 may be determined based on a range in which thephotoacoustic transducer 4 b can detect the photoacoustic wave. In otherwords, in a case where a range in the X direction in which thephotoacoustic transducer 4 b can detect a photoacoustic wave is narrow,the step width of the transducer 4 is made narrow.

Next, in the method (b) in which the photoacoustic signal and theultrasonic signal are both acquired during the stage suspension period,the pulse laser is first irradiated during the stage suspension periodto acquire the photoacoustic signal. After that, the ultrasonic signalsare transmitted and received, and a slice image is acquired. Thoseprocedures may be performed in the opposite order. After the stage ismoved, the same process is repeated. In this method, the amount of onestage moving corresponds to that of such an extent that the volume datacan be created from the slice image generated by the ultrasonic signal,that is, that of the same order of resolution of the slice image. Inthis method, when the information on the inspection object can beobtained only by acquiring the image information at one position, theimage can be obtained while the stage is suspended without being moved.

In the method (c) in which the photoacoustic signal and the ultrasonicsignal are both acquired during the stage moving period, the pulse laserirradiation, the photoacoustic signal acquisition, and the transmissionand reception of the ultrasonic signal are performed during the stagemoving period. In this case, the pulse laser is emitted at an operatingfrequency of ten to several tens hertz, and the transmission andreception of the ultrasonic signal are performed at an operatingfrequency on the order of kilohertz. Therefore, each data is acquiredwith a duty ratio therebetween of approximately 100.

As described above, the stripe width (length in Y direction) of thescanning by the transducer 4 is equal to the width of the photoacoustictransducer 4 b (two-dimensional array) which is the photoacoustic probe.This is because luminance signals within the volume area are calculatedbased on the photoacoustic signals at all positions when an image isreconstructed from the photoacoustic signals. Specifically, in a casewhere the stripe width is thicker than the width of the photoacoustictransducer 4 b, there is a portion which is not inspected. Conversely,in a case where the width of the photoacoustic transducer 4 b is thickerthan the stripe width, there are devices which are not used.Accordingly, an optimum condition for each width is such that the stripewidth and the width of the photoacoustic transducer 4 b are made equalto each other.

On the other hand, when the ultrasonic transducer 4 a which is theultrasonic probe acquires the ultrasonic signal in the stripe, thelength of the one-dimensional array of the ultrasonic transducer 4 aneeds to be made longer than the stripe width.

With reference to FIG. 4, a linear scanning of an ultrasonic beam by theultrasonic transducer 4 a is described. FIG. 4 is a diagram illustratingthe ultrasonic transducer 4 a viewed from the scanning direction (Xdirection) of the transducer 4. In general, one transmission and onereception of an ultrasonic beam 21 are performed by multiple devices.Therefore, a beam center 22 in a Z direction of FIG. 4 inevitably liesinside with respect to an end surface of the probe. Accordingly, anultrasonic image obtained by the ultrasonic transducer 4 a in a beamscanning direction 23 (Y direction) is narrower than the array width ofthe ultrasonic transducer 4 a by an aperture width used for the beamtransmission and reception. Therefore, when the scanning is performedusing a linear probe having the same width as the stripe width, there isa portion in which signals are not acquired between the stripes.

When the aperture for the beam transmission and reception is madesmaller or when a particular method such as steering is used, imaging ispossible also on the end surface of the probe. However, in a case ofusing those methods, methods of forming a beam are different between thecenter of the probe and the end surface thereof, which causesnonuniformity in the resolution and image quality.

Therefore, in this embodiment, the array length of the ultrasonictransducer 4 a is made longer than the stripe width, whereby loss of theultrasonic signals between the stripes can be avoided.

In view of the above, in the transducer 4 according to this embodiment,the length of the ultrasonic transducer 4 a in the directionperpendicular to the scanning direction may be set to be longer than thelength of the photoacoustic transducer 4 b in the directionperpendicular to the scanning direction. The length of the ultrasonictransducer 4 a in the direction perpendicular to the scanning directionmay be made longer at respective longitudinal ends thereof by one halfthe length (aperture width) of the device used for transmitting andreceiving an ultrasonic wave. As a result, when the increased lengths ofthe respective longitudinal ends are added, the total length of theultrasonic transducer 4 a becomes longer by a length equal to theaperture width. In general, the aperture of an ultrasonic beam is formedof several tens of devices, and hence the array length of the ultrasonictransducer 4 a may be set to be longer than the stripe width by a lengthcorresponding to several tens of devices.

FIG. 5 illustrates a state in which a beam generated by the ultrasonictransducer 4 a is focused in a depth direction of the inspection object.The ultrasonic transducer 4 a for transmitting and receiving anultrasonic signal includes an acoustic lens 25 on an entire surfacethereof in order to focus a beam also in a height direction thereof (Zdirection). Similarly to the above-mentioned lateral direction beam, anultrasonic beam is focused while following a locus 24 of FIG. 5.However, a range of acquiring an ultrasonic signal has a certaindistance from immediately below the probe, and hence it is difficult toprevent the ultrasonic beam from spreading. The spreading of theultrasonic beam in this case depends on focus conditions and lensconditions, and may be substantially equal to the height of the probe ormay be wider than the height of the probe.

FIG. 6 illustrates a form of the beam generated by the ultrasonictransducer 4 a. As illustrated in FIG. 6, the width of the beamgenerated by the ultrasonic transducer 4 a exceeds the width of theultrasonic transducer 4 a in a shallower portion and a deeper portion inthe depth direction of the inspection object.

Meanwhile, according to the present invention, the photoacoustictransducer 4 b is provided in a portion close to the ultrasonictransducer 4 a. Therefore, there is a fear that an interference(crosstalk) between the ultrasonic wave from the ultrasonic transducer 4a and the photoacoustic wave detected by the photoacoustic transducer 4b may be generated. Accordingly, in this embodiment of the presentinvention, an interspace is provided between the ultrasonic transducer 4a and the photoacoustic transducer 4 b, whereby the crosstalk can beprevented. The size of the interspace depends on the width of theultrasonic transducer 4 a, the focus conditions, and the like. Forexample, a calculation reveals that there is no problem when theultrasonic transducer 4 a and the photoacoustic transducer 4 b areseparated from each other in the scanning direction by a distancecorresponding to 20% or more of the length of the ultrasonic transducer4 a in the scanning direction.

With the use of the ultrasonic probe described above, all ultrasonicsignals and photoacoustic signals can be acquired within the scanningrange. In the mode described above, the one-dimensional array probe isemployed for acquiring the ultrasonic signal, but the present inventionis not limited thereto. Probes generally referred to as 1.25-dimensionalarray probe, 1.5-dimensional array probe, and 1.75-dimensional arrayprobe, in which devices are further divided in a direction orthogonal tothe array direction, may be employed.

The 1.25-dimensional array probe, in which the devices are divided intoan odd number of parts in the direction orthogonal to the arraydirection, has an aperture control function by switching the otherdevices than a central device. The 1.5-dimensional array probe, in whichthe devices are divided in the direction orthogonal to the arraydirection as in the case of the 1.25-dimensional array probe, is capableof independently controlling a central device and symmetrical devices.The 1.75-dimensional array probe, in which the devices are divided inthe direction orthogonal to the array direction as in the case of the1.25-dimensional array probe, is capable of independently controllingall devices in the direction orthogonal to the array direction. Each ofthe 1.25-dimensional, 1.5-dimensional, and 1.75-dimensional array probesis mounted for improving focusing and steering functions in thedirection orthogonal to the array direction, and the same effect can beobtained by the above-mentioned array probes as in the case where theone-dimensional array probe is employed.

In the mode described above, the one-dimensional array probe is employedfor acquiring the ultrasonic signal and the two-dimensional array probeis employed for acquiring the photoacoustic signal. However, theone-dimensional array probe may be employed for acquiring both theultrasonic signal and the photoacoustic signal. In this case, for therelationship of the array lengths of the probes, similarly to theabove-mentioned mode, the array length of an array probe for acquiringthe ultrasonic signal is set to be longer than the array length of anarray probe for acquiring the photoacoustic signal, thereby obtainingthe same effect.

Second Embodiment Photoacoustic-Ultrasonic System

Next, a photoacoustic-ultrasonic system in which an optical system iscombined with an ultrasonic probe is described. FIG. 7A is a perspectiveview illustrating the photoacoustic-ultrasonic system including theultrasonic probe and the optical system according to this embodiment.

A first probe for transmitting and receiving an ultrasonic wave includesa probe case 30 a, a cable 31 a, and a transducer 4 a. A second probefor receiving a photoacoustic wave includes a probe case 30 b, a cable31 b, and a transducer 4 b. The transducer 4 a is a first array devicecapable of transmitting and receiving the ultrasonic wave. Thetransducer 4 b is a second array device capable of receiving thephotoacoustic wave. A one-dimensional (linear) array is employed for theultrasonic transducer 4 a while a two-dimensional array is employed forthe photoacoustic transducer 4 b.

An optical prism 32 a is provided in an interspace between theultrasonic transducer 4 a and the photoacoustic transducer 4 b. Theoptical prism 32 a serves as an optical system for introducing pulselight emitted from a light source into an inspection object. An opticalprism 32 b may similarly be provided on a side of the second probe,which is opposite to the optical prism 32 a, so as to guide light fromboth sides of the photoacoustic-ultrasonic system. This is because atarget region may need to be irradiated as uniformly as possible due tothe fact that the intensity of the generated photoacoustic wave largelydepends on an irradiation intensity of laser.

FIG. 7B is a cross-sectional view of the photoacoustic-ultrasonic systemaccording to this embodiment, which illustrates incidence of light. Thelight enters a sample as indicated by a broken line of FIG. 7B. Thelight from the light source (not shown) is first guided in a directionperpendicular to a plane on which the two array devices 4 a and 4 b areprovided. The traveling direction of the guided light is changed by theoptical prisms 32 a and 32 b, whereby the light is emitted toward belowthe second array device 4 b.

The optical prism 32 a is provided between the two probes in thismanner. Accordingly, even in a case where the two-dimensional arraydevice 4 b is used, light can be effectively applied to thephotoacoustic transducer 4 b which detects the photoacoustic wave. Inaddition, the two array devices 4 a and 4 b naturally need to be spacedapart from each other, and hence the crosstalk described in the firstembodiment can be prevented.

The space between the two array devices 4 a and 4 b is described. It isunderstood that, in order to realize uniform irradiation as describedabove, the thickness of an optical path needs to be a half or more ofthe width of the photoacoustic transducer 4 b for each side irrespectiveof an irradiation angle of laser. Therefore, an interspace having a sizeequal to at least a half of the width of the photoacoustic transducer 4b needs to be provided between the ultrasonic transducer 4 a and thephotoacoustic transducer 4 b. In other words, the two array devices 4 aand 4 b may be separated from each other in the second direction by adistance corresponding to 50% or more of the length of the second arraydevice in the second direction.

A method of manufacturing the photoacoustic-ultrasonic system accordingto this embodiment is the same as that of the first embodiment, andhence the description thereof is omitted.

In the mode described above, the optical prisms are provided on bothsides of the second probe. However, when optical prisms are provided soas to surround a probe, a more favorable irradiation amount distributioncan be obtained.

Example

Hereinafter, in this example, a case where the probe according to thepresent invention is used for a mammary examination is specificallydescribed. In the mammary examination, it is sufficient that anultrasonic signal and a photoacoustic signal for up to a depth of 4 cmare acquired. The probe used in this case is the probe of FIGS. 1A and1B which is used in the description above.

A laser light intensity allowable to be applied to a human body is 100mJ/cm², and hence a range in which a sufficient photoacoustic signal canbe acquired is 4 cm in depth and 4 cm in width. Accordingly, one side ofa photoacoustic probe was set to 4 cm. Accordingly, one side of thephotoacoustic probe was set to 4 cm. The device pitch was set to 2 mm inconsideration of probe sensitivity and a frequency of 1 MHz to be used,whereby a two-dimensional array probe including 400 devices was formed.An electrostatic capacity type ultrasonic transducer having a band widthof 130% was used as the two-dimensional array probe because thetwo-dimensional array probe is required to detect targets having varioussizes.

On the other hand, with regard to an ultrasonic probe, beam forming wasperformed with a 32-device aperture in order to sufficiently convergebeams. Therefore, the ultrasonic probe is longer than the photoacousticprobe by 16 devices on each of the left and right sides. The totalnumber of devices was set to 192, the device pitch was set to 0.25 mm,the center frequency was set to 10 MHz, and the array length was set to48 mm. Further, an acoustic lens which is formed on a surface of theultrasonic probe had a radius of R8. The beam formed under theabove-mentioned conditions spreads to 7 mm in the vicinities of theultrasonic probe and the vicinities of a depth of 4 cm, and hence aninterspace between the ultrasonic probe and the photoacoustic probe wasset to 1 mm.

Considering that the mamma is scanned using the above-mentioned probes,five strips each having a size of 4 cm×20 cm were formed because thescanning region is 20 cm×20 cm and the stripe width is 4 cm. Thescanning with the probes was performed in a step-and-repeat manner.Laser was applied while the probes were suspended, and the photoacousticsignal was acquired by the two-dimensional array probe. Then, while theprobes were moving, the ultrasonic signal was acquired by theone-dimensional array probe, and an ultrasonic image of each slicesurface was generated and stored as volume data after being subjected toan interpolation processing.

After the scanning of an entire target surface is finished, the image isreconstructed using the photoacoustic signal. A photoacoustic imagegenerated by the reconstruction is accumulated as volume data andsuperimposed on the ultrasonic image. The resultant image is displayedon a screen. The photoacoustic signal and the ultrasonic signal can besuperimposed on each other by the above-mentioned method, with theresult that information containing a morphologic image and a functionalimage can be provided to a user.

In this example, the 32-device aperture for an ultrasonic beam wasadopted. When the size of the aperture is changed according to requiredbeam resolution or a required beam forming method, the same effect canalso be obtained.

The photoacoustic-ultrasonic system illustrated in FIGS. 7A and 7B canalso be used for the mammary examination. In this case, the interspacebetween the ultrasonic probe and the photoacoustic probe needs to be atleast 1.4 mm. On the other hand, in consideration of an incidence angelof 45 degrees and 2 cm which is one half the length of one side of thephotoacoustic probe of 4 cm, the necessary thickness of a prism is 2.83cm, and hence the space between the probes was set to 2.83 cm.

The present invention is not limited to the above embodiments andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore to apprise the public of thescope of the present invention, the following claims are made.

1. An ultrasonic probe, comprising: a first array device capable oftransmitting and receiving an ultrasonic wave; and a second array devicecapable of receiving a photoacoustic wave, wherein the first arraydevice includes a plurality of electromechanical transducers arranged ina first direction; the second array device includes a plurality ofelectromechanical transducers arranged in a two-dimensional manner; andin the first direction, both ends of the first array device lie outsidewith respect to both ends of the second array device.
 2. An ultrasonicprobe according to claim 1, wherein the first array device and thesecond array device are separated from each other in a second directionby a distance corresponding to 20% or more of the length of the firstarray device in the second direction.
 3. An ultrasonic probe accordingto claim 1, wherein the first array device and the second array deviceare separated from each other in a second direction by a distancecorresponding to 50% of the length of the second array device in thesecond direction.
 4. An ultrasonic probe according to claim 1, wherein ascanning direction in which the first array device and the second arraydevice are scanned is perpendicular to the first direction.
 5. Anultrasonic probe according to claim 1, wherein the second array devicecomprises an electrostatic capacity type ultrasonic transducer.
 6. Anultrasonic probe according to claim 1, wherein the first array deviceand the second array device are provided on a same plane.
 7. Anultrasonic probe, comprising: a first array device capable oftransmitting and receiving an ultrasonic wave; and a second array devicecapable of receiving a photoacoustic wave, wherein the first arraydevice includes a plurality of electromechanical transducers arranged ina first direction; the second array device includes a plurality ofelectromechanical transducers arranged in a two-dimensional manner; anultrasonic beam transmitted by the first array device in the firstdirection lies inside with respect to an end surface of the first arraydevice at a focused position; and an imaging range of the first arraydevice is equal to an imaging range of the second array device.
 8. Anultrasonic probe according to claim 7, wherein the first array deviceperforms one transmission of the ultrasonic beam using multiple devices.9. An ultrasonic probe according to claim 7, wherein the first arraydevice and the second array device are provided on a same plane.
 10. Aphotoacoustic-ultrasonic system, comprising: an optical system forintroducing light emitted from a light source into an inspection object;and an ultrasonic probe, comprising: a first array device capable oftransmitting and receiving an ultrasonic wave; and a second array devicecapable of receiving a photoacoustic wave, wherein the first arraydevice includes a plurality of electromechanical transducers, and thesecond array device includes a plurality of electromechanicaltransducers; wherein the optical system is provided in an interspacebetween the first array device and the second array device, and whereinthe optical system is provided so that light guided between a firstprobe including the first array device and a second probe including thesecond array device is emitted from the interspace between the firstarray device and the second array device towards below the second arraydevice.
 11. The photoacoustic-ultrasonic system according to claim 10,wherein the first array device includes the plurality ofelectromechanical transducers arranged in a first direction; and thesecond array device includes the plurality of electromechanicaltransducers arranged in a two-dimensional manner.
 12. Thephotoacoustic-ultrasonic system according to claim 10, wherein the firstarray device and the second array device are provided on a same plane.13. The photoacoustic-ultrasonic system according to claim 10, whereinthe optical system is provided so that light guided between the firstprobe and the second probe intersects a plane on which the second arraydevice is arranged.